Mobile radio communication with various digital modulation techniques group №850-18 Student

5 . DIGITAL MODULATIONS
Digital Modulation Techniques are used to transmit binary data over a band-pass communication channel with fixed frequency limits set by the channel. For wireless data transfer, several digital modulation techniques are incorporated like BPSK, QPSK, DPSK,
OQPSK, BFSK, QAM etc. Among these schemes PSK and QAM are considered to be the most widely used and efficient schemes applied for wireless technology.
5.1 Binary Phase Shift Keying (BPSK)
BPSK or binary PSK is the simplest version of PSK, in which the carrier assumes one of two phases. This scheme has only two signal elements, one with a phase of 0 & the other with phase of 180 (π). A logical 1 is encoded as 0 phase, and a logical 0 is coded as a phase of
π. A bipolar base band signal is treated as the input to the modulator which is then multiplied by a carrier of frequency fc from a local oscillator. If the sinusoidal signal has an amplitude of A and energy per bit the BPSK transmitted signal is ,
Where, is the period of transmitted signal, θ is the phase of the unmodulated carrier & m(t) is the data signal. The modulated signal is multiplied by the recovered carrier, and this product is integrated over a bit interval. If the integration result is positive, the received bit is deemed to be 1; if the integration result is negative, the received bit is deemed to be 0.

Fig. 2: BPSK Modulator
The probability of bit error in an AWGN channel is found using the Q-function of the distance between the signal points and is given by the generalized equation,